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Right before the end of the school year, it finally occurred to me to ask my fourth-grader if she ever drank chocolate milk at school. It turns out she did every day. Her whole table drinks it, she told me at the time — it's one big chocolate-milk party over there. She's a good kid and wants to please her parents, so I told her to please, sweet darling, knock it off. I have my doubts. We try to pack her lunch, but since it's hard to stock small cartons of the whole milk she ravishes at home, we don't have a lot of control over what she drinks in the cafeteria during the school year. Those options are squarely in the hands of the USDA.

Uncle Sam is a very bad uncle when it comes to milk. Minneapolis schools may have ended the practice, but chocolate milk makes up 70 percent of the milk consumed in schools, according to a new report by food activist Michele Simon, and it is even offered right here in Rochester — Healthtown, USA. Thanks to the irreducible relationship linking the U.S. Department of Agriculture with food producers, there are schools in the United States hanging Orwellian posters like "Chocolate Milk Has Muscle" and "Raise Your Hands for Chocolate Milk." In a way, it's hard to argue with the kids. Their alternatives are the deeply unsatisfying skim and the equally nondelicious 1 percent. Still, if you believe sugar is on par with tobacco as a primary factor behind the poor health in our time — and if you haven't, go see the documentary "Fed Up" — you have to ask: How did this happen?

It all happened because of the good intentions of an expert, a Minnesotan whose counterproductive influence on our well-being is becoming increasingly apparent. Besides a fatalistic appeal based on its calcium, chocolate milk in schools is defended on the premise that it is low in fat. Those last three words are proving to be the great delusion of our times. As "The Big Fat Surprise," an unflinching new book by the journalist Nina Teicholz, makes clear, by allowing a Minnesotan-led clique of experts to set our dietary policy against saturated fat 50 years ago, we placed ourselves on a path to becoming fatter and sicker than ever.

We embraced the erroneous low-fat paradigm because a University of Minnesota-based expert named Ancel Keys had a gut feeling that saturated fat caused heart disease; collected carefully chosen data from dietary practices in Greece and Italy to back up his hunch, then brushed off all contrary evidence. Keys quickly developed alliances at the American Heart Association and the National Institutes of Health, on Capitol Hill and at the USDA — with the help of an eager and unquestioning health press much like that of today. (Time magazine placed him on its cover, and this was back when people still read Time magazine.) In a less-known Minnesota connection to the tale, Teicholz describes how the largest-ever trial of the Keys hypothesis was conducted here in the 1960s. Most doctors do not know about the 9,000-patient Minnesota Coronary Survey, however, and that's because it failed to find that cutting saturated fat reduced the risk of heart disease — whereupon the author kept the results to himself for 16 years. This is how science is treated in the dietary policy world: as publicity to be either promoted or suppressed depending upon what it finds.

Popular books on diet are often padded with recipes and platitudes, but Teicholz's parsing of the force that was Keys and the fad science he set in motion is a substantive, decade-in-the-making work of synthesis and argument, a book that is cultural in its questions and that has drilled deep into the poor data used to justify the way we have been told to eat — ideas that are currently messing up my daughter's lunchroom. Simply out of institutional atonement, "Big Fat Surprise" should become mandatory reading in every science class on the sprawling University of Minnesota campus. The book opens with a strange curiosity: The Inuit tossed the tenderloin of caribou they ate to their dogs. During the period they were studied at the turn of the century, the native people of the Arctic got 70 percent to 80 percent of their calories from fat, a meal plan that included no plants. According to Keys theory, the Inuit should have had hearts like ICU patients, but by 1951 a German doctor who studied the population would find no signs of cancer, diabetes, heart disease or hypertension. In a separate example, the Maasai warriors of Kenya ate only blood, meat and milk during a period in which they were studied in the early 1960s, yet had no heart disease or high cholesterol.

"On the surface, these stories from the Arctic and Africa … seem paradoxical, given what we think we know about animal fats and heart attack risk," writes Teicholz, a carnivore who recently took a cholesterol profile for "Nightline" and learned that her numbers are better than when she was eating low-fat foods back in the 1990s. "Good health and high consumption of animal fats should be mutually exclusive." According to the Keys logic, "dietary fat caused cholesterol to rise, which would eventually harden arteries and lead to a heart attack," as she writes. "It turns out every step in this chain of events has failed to be substantiated."

Gary Taubes reported large portions of this still surprising material in his 2007 book "Good Calories, Bad Calories," but Teicholz describes the human story of how bad science became federal policy, especially concerning the question of heart disease. She also may have picked a better moment for the good news about bacon: A recent essay in the journal BMJ argued that "Saturated Fat is Not the Major Issue," and a sprawling meta-analysis published in the Annals of Internal Medicine recently found no evidence of harm caused by eating saturated fats. The idea that Keys cherrypicked his data has been documented elsewhere, but Teicholz supplies the deed with a banquet of human detail.

When she asks a Keys contemporary why the biologist did not study diet and heart disease in butter-consuming France or cheese-eating Switzerland, she learns how "Keys just had a personal aversion to being in France and Switzerland." She relays how good weather very likely influenced his choice of which diet to highlight — that his spirits lifted upon leaving behind the cold weather and rationed food where he had been teaching in Oxford, England. We learn how Keys ate steaks, chops and roasts three times a week while advocating a diet limited to 7 percent saturated fat. We learn how he conducted his research on the Mediterranean diet during an era of hardship following World War II, much of it during the meat-sparing season of Lent. And that he threw out the results he didn't like from more than 600 questionnaires, leaving just 33 Cretans and another 34 men from Corfu as the basis for our entire dietary reversal.

Less-rigid dietary experts will often counter that butter in moderation may be fine, but that the "Mediterranean diet" is still preferable. "All things in moderation" is the great hiding place for those faced with discordant findings in dietary science, and the phrase is in heavy play these days. It might surprise the moderation-minded to read in "Big Fat Surprise" that olive oil gained its current fame thanks to a lot of gracious industry-sponsored press junkets; that it is less healthful for your good cholesterol than steak or whole milk, and that the Mediterranean diet may be neither Mediterranean nor demonstrably superior in terms of heart health.

Moreover, by shunning animal fats (undeservedly) and trans fats (deservedly), the changes of the past five decades have led us into uncharted waters. Lard was healthy for frying, but now food companies that are worried about the stigma of mandatory saturated-fat levels on food labels are cooking with seed and vegetable oils that oxidize at high heat, easily turn rancid and leave solids inside of fryers that require special industrial cleaning techniques. "The case against saturated fat has collapsed," Teicholz writes, and late enough in the book to offer the brazen advice that follows: "Eat butter; drink milk whole, and feed it to the whole family. Stock up on creamy cheeses, offal, and sausage and yes, bacon. None of these foods have been demonstrated to cause obesity, diabetes or heart disease."

Good facts to know. Now can someone please offer my child an ordinary glass of milk?

Paul John Scott is a health-sciences writer living in Rochester. On Twitter: @pauljohnscott.